Method in which a receiver transmits control information in a wireless communication system

ABSTRACT

The present invention relates to a method in which a receiver transmits control information in a wireless communication system. The method comprises a step of receiving a plurality of data units from a transmitter, a step of determining acknowledgement/negative-acknowledgement (ACK/NACK) states for each of the data units; and a step of transmitting, to the transmitter, the ACK/NACK states in multiple ACK/NACK states or in a single ACK/NACK state in accordance with a predetermined condition.

This application is the National Phase of PCT/KR2010/004497 filed onJul. 9, 2010, which claims priority under 35 U.S.C. 119(e) to U.S.Provisional Application No. 61/225,924 filed on Jul. 16, 2009, all ofwhich are hereby expressly incorporated by reference into the presentapplication.

TECHNICAL FIELD

The present invention relates to a method for allowing a receiver totransmit control information in a wireless communication system, andmore particularly, to a method for efficiently transmitting controlinformation such as ACK/NACK signal and an apparatus for the same.

BACKGROUND ART

A wireless communication system has been widely developed to providevarious kinds of communication services such as voice and data.Generally, the wireless communication system is a multiple access systemthat can support communication with multiple users by sharing availablesystem resources (bandwidth, transmission power, etc.). Examples of themultiple access system include a code division multiple access (CDMA)system, a frequency division multiple access (FDMA) system, a timedivision multiple access (TDMA) system, an orthogonal frequency divisionmultiple access (OFDMA) system, a single carrier frequency divisionmultiple access (SC-FDMA) system, and a multi carrier-frequency divisionmultiple access (MC-FDMA) system. In the wireless communication system,a user equipment may receive information from a base station through adownlink, and may transmit information to the base station through anuplink. Examples of information transmitted from or received in the userequipment include data and various kinds of control information. Variousphysical channels exist depending on a type and usage of the informationtransmitted from or received in the user equipment.

In the wireless communication system, since a channel between atransmitter and a receiver is not fixed, it is required to frequentlymeasure a channel between a transmitting antenna and a receivingantenna. If the transmitter and the receiver transmit and receive asignal mutually prescribed to and from each other to measure a channel,a phase shifted value and a decreasing amount of amplitude caused by thechannel may be identified. And, the identified information may be fedback to a transmitting side. Alternatively, data information which isnot prescribed may reliably be detected and decoded using the identifiedinformation. The signal prescribed between the transmitter and thereceiver may be referred to as a reference signal, a pilot signal or asounding reference signal.

A 3^(rd) generation partnership project long term evolution (3GPP LTE)communication system which is an example of a mobile communicationsystem to which the present invention can be applied will be describedin brief.

FIG. 1 is a diagram illustrating a network structure of an EvolvedUniversal Mobile Telecommunications System (E-UMTS) which is an exampleof a mobile communication system. The E-UMTS is an evolved version ofthe conventional UMTS, and its basic standardization is in progressunder the 3rd Generation Partnership Project (3GPP). The E-UMTS maygenerally be referred to as a Long Term Evolution (LTE) system. Fordetails of the technical specifications of the UMTS and E-UMTS, refer toRelease 7 and Release 8 of “3rd Generation Partnership Project;Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE) 120, basestations (eNode B and eNB) 110 a and 110 b, and an Access Gateway (AG)which is located at an end of a network (E-UTRAN) and connected to anexternal network. Generally, the base stations may simultaneouslytransmit multiple data streams for a broadcast service, a multicastservice and/or a unicast service.

One or more cells may exist for one base station. One cell is set to oneof bandwidths of 1.25, 2.5, 5, 10, and 20 MHz to provide a downlink oruplink transport service to several user equipments. Different cells maybe set to provide different bandwidths. Also, one base station controlsdata transmission and reception for a plurality of user equipments. Thebase station transmits downlink (DL) scheduling information of downlinkdata to the corresponding user equipment to notify the user equipment oftime and frequency domains to which data will be transmitted andinformation related to encoding, data size, hybrid automatic repeat andrequest (HARQ). Also, the base station transmits uplink (UL) schedulinginformation of uplink data to the corresponding user equipment to notifythe user equipment of time and frequency domains that can be used by thecorresponding user equipment, and information related to encoding, datasize, and HARQ. An interface for transmitting user traffic or controltraffic may be used between the base stations. A Core Network (CN) mayinclude the AG and a network node or the like for user registration ofthe user equipment UE. The AG manages mobility of the user equipment UEon a Tracking Area (TA) basis, wherein one TA includes a plurality ofcells.

Although the wireless communication technology developed based on WCDMAhas been evolved into LTE, request and expectation of users andproviders have continued to increase. Also, since another wirelessaccess technology is being continuously developed, new evolution of thewireless communication technology will be required for competitivenessin the future. In this respect, reduction of cost per bit, increase ofavailable service, use of adaptable frequency band, simple structure,open type interface, proper power consumption of the user equipment,etc. are required.

Recently, standardization of advanced technology of LTE is in progressunder the 3rd Generation Partnership Project (3GPP). This technologywill be referred to as “LTE-Advanced” or “LTE-A.” One of importantdifferences between the LTE system and the LTE-A system is difference insystem bandwidth. The LTE-A system aims to support a wideband of maximum100 MHz. To this end, the LTE-A system uses carrier aggregation orbandwidth aggregation that achieves a wideband using a plurality offrequency blocks. For wider frequency bandwidth, carrier aggregationaims to use a plurality of frequency blocks as one great logicalfrequency band. A bandwidth of each frequency block may be defined basedon a bandwidth of a system block used in the LTE system. Each frequencyblock is transmitted using a component carrier.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the conventionalproblem is to provide to a method for efficiently transmitting feedbackinformation from a receiver to a transmitter by reducing feedbackinformation.

Another object of the present invention is to provide a method forefficiently managing resources by reducing a control channel resourceused for feedback information transmission, whereby resources used fordata transmission can be increased.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present invention are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present invention could achieve will be more clearlyunderstood from the following detailed description.

Technical Solution

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein,according to one embodiment of the present invention, a method fortransmitting control information from a receiver in a wirelesscommunication system comprises the steps of receiving a plurality ofdata units from a transmitter; determiningacknowledgement/negative-acknowledgement (ACK/NACK) states for each ofthe data units; and transmitting, to the transmitter, the ACK/NACKstates in multiple ACK/NACK states or in a single ACK/NACK state inaccordance with a predetermined condition.

The plurality of ACK/NACK states may be configured in the single NACKstate when the plurality of ACK/NACK states include more than a certainnumber of NACKs.

The plurality of data units may be received through a plurality ofcarriers.

The plurality of ACK/NACK states may be configured in the multipleACK/NACK states or the single ACK/NACK state on the basis of carriergroup.

At this time, the control information may be configured per carrier, andcontrol information transmitted through different carriers depending ona type of each of the plurality of carriers may be multiplexed on thebasis of the carrier group.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein,according to another embodiment of the present invention, a receiver ina wireless communication system comprises a reception (Rx) module forreceiving a plurality of data units from a transmitter; a transmission(Tx) module for transmitting radio frequency (RF) signals to thetransmitter; and a processor determiningacknowledgement/negative-acknowledgement (ACK/NACK) states for each ofthe data units received through the Rx module, wherein the processorconfigures the ACK/NACK states in multiple ACK/NACK states or in asingle ACK/NACK state in accordance with a predetermined condition andtransmits the ACK/NACK states to the transmitter through the Tx module.

The processor may configure the plurality of ACK/NACK states in thesingle NACK state when the plurality of ACK/NACK states include morethan a certain number of NACKs.

Also, the processor may configure the plurality of ACK/NACK states inthe multiple ACK/NACK states or the single ACK/NACK state on the basisof carrier group.

The aforementioned embodiments of the present invention are only a partof the preferred embodiments of the present invention, and variousembodiments in which technical features of the present invention arereflected may be devised and understood based on the detaileddescription of the present invention, which will be described later, bythe person with ordinary skill in the art.

Advantageous Effects

According to the embodiments of the present invention, the receiver mayefficiently transmit feedback information to the transmitter by reducinga feedback information rate.

In addition, according to the embodiments of the present invention, acontrol channel resource used for feedback transmission from thereceiver to the transmitter may be reduced to efficiently manageresources, whereby a resource used for other data transmission may beincreased.

It will be appreciated by persons skilled in the art that that theeffects that could be achieved with the present invention are notlimited to what has been particularly described hereinabove and otheradvantages of the present invention will be more clearly understood fromthe following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a diagram illustrating a network structure of an EvolvedUniversal Mobile Telecommunications System (E-UMTS) which is an exampleof a mobile communication system;

FIG. 2 is a diagram illustrating a structure of a radio frame used in a3GPP LTE system;

FIG. 3 is a diagram illustrating physical channels used in a 3GPP LTEsystem and signal transmission using the physical channels;

FIG. 4 is a diagram illustrating a structure of a downlink subframe;

FIG. 5 is a diagram illustrating a time-frequency resource gridstructure of a downlink slot used in a 3GPP LTE system;

FIG. 6 is a diagram illustrating a structure of an uplink subframe usedin an LTE system;

FIG. 7 is a diagram illustrating a PUCCH structure for ACK/NACKtransmission;

FIG. 8 is a diagram illustrating an example of determining a PUCCHresource for ACK/NACK;

FIG. 9 is a diagram illustrating an example of communication performedunder multiple component carriers;

FIG. 10 is a flow chart illustrating an example of a procedure oftransmitting feedback information by determining ACK/NACK state inaccordance with one embodiment of the present invention;

FIG. 11 is a diagram illustrating an example of a plurality of downlinkcarriers aggregated for feedback information transmission according toanother embodiment of the present invention;

FIG. 12 is a diagram illustrating another example of a plurality ofdownlink carriers aggregated for feedback information transmissionaccording to another embodiment of the present invention;

FIG. 13 is a diagram illustrating other example of a plurality ofdownlink carriers aggregated for feedback information transmissionaccording to another embodiment of the present invention; and

FIG. 14 is a diagram illustrating a base station and a user equipment,through which the embodiments of the present invention can be carriedout.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings. It is to beunderstood that the detailed description, which will be disclosed alongwith the accompanying drawings, is intended to describe the exemplaryembodiments of the present invention, and is not intended to describe aunique embodiment with which the present invention can be carried out.The following detailed description includes detailed matters to providefull understanding of the present invention. However, it will beapparent to those skilled in the art that the present invention can becarried out without the detailed matters. For example, although thefollowing description will be made based on a mobile communicationsystem of a 3GPP LTE system, the following description may be applied toother mobile communication systems except for unique features of the3GPP LTE system.

In some cases, to prevent the concept of the present invention frombeing ambiguous, structures and apparatuses of the known art will beomitted, or will be shown in the form of a block diagram based on mainfunctions of each structure and apparatus. Also, wherever possible, thesame reference numbers will be used throughout the drawings and thespecification to refer to the same or like parts.

Furthermore, in the following description, it is assumed that a userequipment means a mobile or fixed type user terminal such as a mobilestation (MS). It is also assumed that a base station means a random nodeof a network node, such as Node B and eNode B, which performscommunication with a user equipment.

The following technology may be used for various wireless access systemssuch as code division multiple access (CDMA), frequency divisionmultiple access (FDMA), time division multiplex access (TDMA),orthogonal frequency division multiple access (OFDMA), and singlecarrier frequency division multiple access (SC-FDMA). The CDMA may beimplemented by radio technology such as universal terrestrial radioaccess (UTRA) or CDMA2000. The TDMA may be implemented by radiotechnology such as global system for mobile communications (GSM)/generalpacket radio service (GPRS)/enhanced data rates for GSM evolution(EDGE). The OFDMA may be implemented by radio technology such as IEEE802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, and evolved UTRA(E-UTRA). The UTRA is a part of a universal mobile telecommunicationssystem (UMTS). A 3rd generation partnership project long term evolution(3GPP LTE) communication system is a part of an evolved UMTS (E-UMTS)that uses E-UTRA, and uses OFDMA on a downlink and SC-FDMA on an uplink.LTE-advanced (LTE-A) is an evolved version of the 3GPP LTE.

To clarify description of the present invention, although the presentinvention will be described based on 3GPP LTE/LTE-A, it is to beunderstood that technical features of the present invention are notlimited to the 3GPP LTE/LTE-A.

In a wireless communication system, a user equipment may receiveinformation from a base station through a downlink, and may alsotransmit information to the base station through an uplink. Examples ofinformation transmitted from or received in the user equipment includedata and various kinds of control information. Various physical channelsexist depending on a type and usage of the information transmitted fromor received in the user equipment.

FIG. 2 is a diagram illustrating a structure of a radio frame used in anLTE system.

Referring to FIG. 2, the radio frame has a length of 10 ms(327200·T_(s)) and includes ten (10) subframes of an equal size. Eachsubframe has a length of 1 ms and includes two slots each having alength of 0.5 ms. In this case, T_(s) represents a sampling time, and isexpressed by T_(s)=1/(15 kHz×2048)=3.2552×10⁻⁸ (about 33 ns). The slotincludes a plurality of OFDM symbols (or SC-FDMA symbols) in a timedomain, and includes a plurality of resource blocks (RBs) in a frequencydomain. In the LTE system, one resource block includes twelve (12)subcarriers×seven (or six) OFDM (or SC-FDMA) symbols. A frame structuretype-2 includes two half frames, each of which includes five subframes,a downlink piloting time slot (DwPTS), a guard period (GP), and anuplink piloting time slot (UpPTS). The aforementioned structure of theradio frame is only exemplary, and various modifications may be made inthe number of subframes included in the radio frame or the number ofslots included in the subframe, or the number of OFDM (or SC-FDMA)symbols included in the slot.

FIG. 3 is a diagram illustrating physical channels used in an LTE systemand signal transmission using the physical channels.

Referring to FIG. 3, the user equipment performs initial cell searchsuch as synchronizing with the base station when it newly enters a cellor the power is turned on (S310). To this end, the user equipment maysynchronize with the base station by receiving a primary synchronizationchannel (P-SCH) and a secondary synchronization channel (S-SCH) from thebase station, and may acquire information such as cell ID, etc.Afterwards, the user equipment may acquire broadcast information withinthe cell by receiving a physical broadcast channel (PBCH) from the basestation. Meanwhile, the user equipment may identify a downlink channelstatus by receiving a downlink reference signal at the initial cellsearch step.

The user equipment which has finished the initial cell search mayacquire more detailed system information by receiving a physicaldownlink shared channel (PDSCH) in accordance with a physical downlinkcontrol channel (PDCCH) and information carried in the PDCCH (S320).

Meanwhile, if the user equipment initially accesses the base station, orif there is no radio resource for signal transmission, the userequipment may perform a random access procedure (RACH) for the basestation (S330 to S360). To this end, the user equipment may transmit apreamble of a specific sequence through a physical random access channel(PRACH) (S330 and S350), and may receive a response message to thepreamble through the PDCCH and the PDSCH corresponding to the PDCCH(S340 and S360). In case of a contention based RACH, a contentionresolution procedure may be performed additionally.

The user equipment which has performed the aforementioned steps mayreceive the PDCCH/PDSCH (S370) and transmit a physical uplink sharedchannel (PUSCH) and a physical uplink control channel (PUCCH) (S380), asa general procedure of transmitting uplink/downlink signals. Controlinformation transmitted from the user equipment to the base station orreceived from the base station to the user equipment through the uplinkincludes downlink/uplink ACK/NACK signals, a channel quality indicator(CQI), a precoding matrix index (PMI), and a rank indicator (RI). Incase of the 3GPP LTE system, the user equipment may transmit theaforementioned control information such as CQI/PMI/RI through the PUSCHand/or the PUCCH.

FIG. 4 is a diagram illustrating a structure of a downlink subframe.

Referring to FIG. 4, one subframe includes two slots in a time domain.Maximum three OFDM symbols located at the front of the first slot of thesubframe correspond to a control region to which control channels areallocated. The other OFDM symbols correspond to a data region to which aphysical downlink shared channel (PDSCH) is allocated.

Examples of the downlink control channel used in the 3GPP LTE include aPhysical Control Format Indicator Channel (PCFICH), a Physical DownlinkControl Channel (PDCCH), and a Physical Hybrid ARQ Indicator Channel(PHICH). The PCFICH is transmitted from the first OFDM symbol of thesubframe, and carries information on the number (that is, size ofcontrol region) of OFDM symbols used for transmission of the controlchannels within the subframe. The control information transmittedthrough the PDCCH will be referred to as downlink control information(DCI). The DCI includes uplink resource allocation information, downlinkresource allocation information, uplink transmission (Tx) power controlcommand for random user equipment groups, etc. The PHICH carries HARQACK/NACK (acknowledgement/negative-acknowledgement) in response touplink HARQ. In other words, the ACK/NACK signal for uplink datatransmitted from the user equipment is transmitted onto the PHICH.

Hereinafter, the PDCCH will be described.

The PDCCH may carry resource allocation and transport format (may bereferred to as downlink grant) of the PDSCH, resource allocationinformation (may be referred to as uplink grant) of the PUSCH,aggregation of transmission power control commands of individual userequipments (UEs) within a random user equipment group, and activityindication information of voice over Internet protocol (VoIP). Aplurality of PDCCHs may be transmitted within the control region. Theuser equipment may monitor the plurality of PDCCHs. The PDCCH iscomprised of aggregation of one or a plurality of continuous controlchannel elements (CCEs). The PDCCH comprised of aggregation of one or aplurality of continuous CCEs may be transmitted through the controlregion after subblong interleaving. The CCE is a logic allocation unitused to provide a coding rate based on the status of a radio channel tothe PDCCH. The CCE corresponds to a plurality of resource element groups(REGs). The format of the PDCCH and the number of available bits of thePDCCH are determined depending on correlation between the number of CCEsand the coding rate provided by the CCEs.

The control information transmitted through the PDCCH will be referredto as downlink control information (DCI). The following Table 1illustrates the DCI based on a DCI format.

TABLE 1 DCI Format Description DCI format 0 used for the scheduling ofPUSCH DCI format 1 used for the scheduling of one PDSCH codeword DCIformat 1A used for the compact scheduling of one PDSCH codeword andrandom access procedure initiated by a PDCCH order DCI format 1B usedfor the compact scheduling of one PDSCH codeword with precodinginformation DCI format 1C used for very compact scheduling of one PDSCHcodeword DCI format 1D used for the compact scheduling of one PDSCHcodeword with precoding and power offset information DCI format 2 usedfor scheduling PDSCH to UEs configured in closed- loop spatialmultiplexing mode DCI format 2A used for scheduling PDSCH to UEsconfigured in open- loop spatial multiplexing mode DCI format 3 used forthe transmission of TPC commands for PUCCH and PUSCH with 2-bit poweradjustments DCI format 3A used for the transmission of TPC commands forPUCCH and PUSCH with single bit power adjustments

The DCI format 0 represents uplink resource allocation information, theDCI formats 1 and 2 represent downlink resource allocation information,and the DCI formats 3 and 3A represent uplink transmit power control(TPC) command for random user equipment groups.

FIG. 5 is a diagram illustrating a time-frequency resource gridstructure of a downlink slot used in a 3GPP LTE system which is anexample of a mobile communication system.

Referring to FIG. 5, a downlink signal transmitted from each slot may beexpressed by a resource grid as shown in FIG. 1, which includes N_(RB)^(DL)×N_(sc) ^(RB) number of subcarriers and N_(symb) ^(DL) number ofOFDM (orthogonal frequency division multiplexing) symbols. In this case,N_(RB) ^(DL) represents the number of resource blocks (RBs) in thedownlink, N_(sc) ^(RB) represents the number of subcarriers thatconstitute one resource block (RB), and N_(symb) ^(DL) represents thenumber of OFDM symbols at one downlink slot. The size of N_(RB) ^(DL)may be varied depending on a downlink transmission bandwidth configuredwithin a cell and should satisfy N_(RB) ^(min,DL)≦N_(RB) ^(DL)≦N_(RB)^(max,DL). In this case, N_(RB) ^(min,DL) is the smallest downlinkbandwidth supported by the wireless communication system, and N_(RB)^(max,DL) is the greatest downlink bandwidth supported by the wirelesscommunication system. Although N_(RB) ^(min,DL)=6 and N_(RB)^(max,DL)=110 may be provided, the present invention is not limited tothis example. The number of OFDM symbols included in one slot may bevaried depending on a length of cyclic prefix (CP) and interval of thesubcarriers. In case of MIMO antenna transmission, one resource grid maybe defined per one antenna port.

Each element within the resource grid for each antenna port is referredto as a resource element (RE), and is uniquely identified by a pair ofindexes within the slot. In this case, k is an index in a frequencydomain, l is an index in a time domain. Also, k has any one value of 0,. . . , N_(RB) ^(DL)N_(sc) ^(RB)−1, and l has any one value of 0, . . ., N_(symb) ^(DL)−1.

If the time-frequency resource grid structure shown in FIG. 5 is appliedto the uplink, each symbol may be referred to as SC-FDMA symbol.

FIG. 6 is a diagram illustrating a structure of an uplink subframe inthe LTE.

Referring to FIG. 6, the uplink subframe includes a plurality of slots(for example, two slots). The uplink subframe is divided into a dataregion and a control region on the frequency domain. The data regionincludes a physical uplink shared channel (PUSCH), and is used totransmit a data signal such as voice and video. The control regionincludes a physical uplink control channel (PUCCH), and is used totransmit control information. The PUCCH includes RB pair located at bothends of the data region on a frequency axis, and performs hopping on theborder of the slots. The control information includes Hybrid AutomaticRetransmit reQuest (HARQ) ACK/NACK.

FIG. 7 is a diagram illustrating a structure of a physical uplinkcontrol channel (PUCCH) resource for ACK/NACK transmission.

Referring to FIG. 7, in case of a normal cyclic prefix (CP), a referencesignal (UL RS) is carried in three continuous symbols located at thecenter of the slot, and control information (i.e., ACK/NACK) is carriedin the other four symbols. In case of an extended CP, the slot includessix symbols, wherein a reference signal is carried in the third andfourth symbols. The ACK/NACK from several user equipments is multiplexedwith one PUCCH resource by using a CDM mode. The CDM mode is implementedusing cyclic shift (CS) of a sequence for frequency spreading and/or(pseudo)orthogonal spreading code for time spreading. For example, theACK/NACK identified using different cyclic shifts (CS) (frequencyspreading) of computer generated constant amplitude zero autocorrelation (CG-CAZAC) sequence and/or different walsh/DFT orthogonalcodes (time spreading). w0, w1, w2, w3 multiplied after IFFT obtain thesame result even though they are multiplied before IFFT. In the LTEsystem, the PUCCH resources for transmitting ACK/NACK are expressed bycombination of the cyclic shift of the sequence for frequency spreadingand the (pseudo)orthogonal spreading code for time spreading and thelocation of the frequency-time resource (for example, resource block),and each PUCCH resource is indicated using a PUCCH (resource) index.

FIG. 8 is a diagram illustrating an example of determining PUCCHresources for ACK/NACK.

In the LTE system, PUCCH resources for ACK/NACK are not previouslyallocated to each user equipment but used per timing point by aplurality of user equipments within a cell. In more detail, the PUCCHresources used for ACK/NACK transmission by the user equipmentcorrespond to PDCCH carrying scheduling information of correspondingdownlink data. In each downlink subframe, an entire region where thePDCCH is transmitted includes a plurality of control channel elements(CCEs), and the PDCCH transmitted to the user equipment includes one ormore CCEs. The user equipment transmits ACK/NACK through a PUCCHresource corresponding to a specific CCE (for example, first CCE) amongCCEs constituting PDCCH received therein.

Referring to FIG. 8, each square block in a downlink represents a CCE,and each square block in an uplink represents a PUCCH resource. EachPUCCH index corresponds to a PUCCH resource for ACK/NACK. It is assumedthat PDSCH information is transferred through a PDCCH that includes CCEsNos. 4 to 6 as illustrated in FIG. 8. In this case, the user equipmenttransmits ACK/NACK through PUCCH No. 4 corresponding to CCE No. 4 whichis the first CCE of the PDCCH. FIG. 8 illustrates that maximum M numberof PUCCHs exist in the uplink (UL) when maximum N number of CCEs existin the downlink (DL). Although N may be equal to M (N=M), M may bedesigned to differ from N, and mapping between CCEs and PUCCHs may beoverlapped.

In more detail, in the LTE system, the PUCCH resource index is definedas follows.n ⁽¹⁾ _(PUCCH) =n _(CCE) +N ⁽¹⁾ _(PUCCH)  [Equation 1]

In this case, n⁽¹⁾ _(PUCCH) represents a PUCCH resource index fortransmitting ACK/NACK, N⁽¹⁾ _(PUCCH) represents a signaling valuetransferred from an upper layer, and n_(CCE) represents the smallestvalue of CCE indexes used for PDCCH transmission.

As expressed by the Equation 1, the PUCCH index for ACK/NACKtransmission is determined in accordance with the first CCE for PDCCHtransmission. Then, resource block (RB) index for PUCCH transmission,orthogonal cover index and cyclic shift value are determined using thePUCCH index. Since the base station reserves the PUCCH resource as muchas the number of CCEs used for PDCCH transmission, if the CCEs used forPDCCH transmission are two or more, the PUCCH index mapped into theother CCEs except for the first CCE is not used for PUCCH transmission.

FIG. 9 is a diagram illustrating an example of communication performedunder multiple component carriers.

FIG. 9 may correspond to a communication example of the LTE-A system.The LTE-A system uses carrier aggregation or bandwidth aggregation wherea plurality of uplink/downlink frequency blocks are collected to usebroader frequency bandwidths, thereby using greater uplink/downlinkbandwidths. Each frequency block is transmitted using a componentcarrier (CC). In this specification, the component carrier may mean afrequency block for carrier aggregation or a central carrier of thefrequency block depending on the context. The frequency block forcarrier aggregation and the central carrier of the frequency block maybe used together.

Referring to FIG. 9, five component carriers (CCs) of 20 MHz arecollected in the uplink/downlink to support a bandwidth of 100 MHz. Therespective component carriers may adjoin each other in the frequencydomain or not. For convenience, FIG. 9 illustrates that a bandwidth ofeach uplink component carrier is the same as and symmetrical to that ofeach downlink component carrier. However, the bandwidths of therespective component carriers may be defined independently. For example,the bandwidths of the uplink component carriers may be configured as 5MHz (UL CC0)+20 MHz (UL CC1)+20 MHz (UL CC2)+20 MHz (UL CC3)+5 MHz (ULCC4). Also, asymmetrical carrier aggregation where the number of uplinkcomponent carriers is different from the number of downlink componentcarriers may be configured.

The asymmetrical carrier aggregation may occur due to a limit ofavailable frequency bandwidth, or may be configured artificially bynetwork configuration. For example, even though N number of CCs areconfigured in the entire system band, a frequency band that can bereceived by a specific user equipment may be limited to M(<N) number ofCCs. Various parameters for carrier aggregation may be setcell-specifically, UE group-specifically or UE-specifically.

Also, although FIG. 9 illustrates that an uplink signal and a downlinksignal are transmitted through component carriers mapped with each otherone to one, the component carrier through which a signal is actuallytransmitted may be varied depending on network configuration or signaltype. For example, if a scheduling command is downlink-transmittedthrough the DL CC1, the data based on the scheduling command may beperformed through another DL CC or UL CC. Also, control informationrelated to the DL CC may be uplink-transmitted through a specific UL CCregardless of mapping between the component carriers. Similarly,downlink control information may be transmitted through a specific DLCC.

A Tx node may transmit a plurality of data units to an Rx node within agiven physical resource, and the Rx node may transmit a plurality ofcorresponding ACK/NACK signals within the given physical resource. Thephysical resource includes frequency, time, space, code or their randomcombination. For description of the present invention, it is assumedthat the Rx node transmits ACK/NACK corresponding to each data unitthrough unit ACK/NACK resource. For convenience, the unit ACK/NACKresource will simply be referred to as ACK/NACK. For example, theACK/NACK unit includes a PUCCH resource for ACK/NACK transmission.Meanwhile, the number of ACK/NACK signals to be transmitted through oneUL subframe may be increased for some reasons (for example, asynchronouscarrier aggregation, TDD mode, relay backhaul link, etc.) In this case,since the Rx node transmits ACK/NACK signals through a plurality ofACK/NACK units, ACK/NACK transmission and reception may be complicatedand the total ACK/NACK transmission power may be increased. In order toprevent a large number of ACK/NACK signals from being transmittedthrough the plurality of ACK/NACK units and reduce the total ACK/NACKtransmission power, the following methods may be considered.

1) ACK/NACK Bundling

In ACK/NACK bundling, ACK/NACK responses to a plurality of data unitsare combined with one another by logical-AND operation. For example, theRx node transmits ACK signal by using one ACK/NACK unit if all the dataunits are successfully decoded. On the other hand, the Rx node transmitsNACK signal by using one ACK/NACK unit or does not transmit any signalif decoding (or detection) is failed even in any one of the data units.

2) ACK/NACK Multiplexing

In ACK/NACK multiplexing, ACK/NACK responses to a plurality of dataunits are identified by combination of ACK/NACK unit used for actualACK/NACK transmission and the transmitted ACK/NACK message. For example,it is assumed that the ACK/NACK unit carries two bits and maximum twodata units are transmitted. In other words, we assume that HARQoperation for each data unit can be managed by a single ACK/NACK bit. Inthis case, the ACK/NACK result may be identified by the Tx node asexpressed by Table 2.

TABLE 2 HARQ-ACK(0), HARQ-ACK (1) n_(PUCCH) ⁽¹⁾ b(0), b(1) ACK, ACKn_(PUCCH, 1) ⁽¹⁾ 1, 1 ACK, NACK/DTX n_(PUCCH, 0) ⁽¹⁾ 0, 1 NACK/DTX, ACKn_(PUCCH, 1) ⁽¹⁾ 0, 0 NACK/DTX, NACK n_(PUCCH, 1) ⁽¹⁾ 1, 0 NACK, DTXn_(PUCCH, 0) ⁽¹⁾ 1, 0 DTX, DTX N/A N/A

In Table 2, HARQ-ACK(i) represents the ACK/NACK result for the data uniti. DTX (Discontinuous Transmission) represents that there are no datatransmitted for the corresponding HARQ-ACK(i) or the Rx node fails todetect the data unit corresponding to HARQ-ACK(i). NACK/DTX representsthat NACK and DTX are coupled with each other. In other words, NACK/DTXrepresents the ACK/NACK result is NACK or DTX only. n(1)PUCCH, Xrepresents ACK/NACK unit to be used for actual ACK/NACK transmission,and maximum two ACK/NACK units (that is, n(1)PUCCH,0 and n(1)PUCCH,1)exist. b(0),b(1) represent two bits carried by the selected ACK/NACKunit. For example, if the Rx node receives two data units andsuccessfully decodes them, it transmits two bits (1,1) by using theACK/NACK unit n(1)PUCCH,1. Although the Tx node has transmitted two dataunits, if the Rx node fails to decode the first data unit (correspondingto HARQ-ACK(0)) and successfully decodes the second data unit(corresponding to HARQ-ACK(1)), it transmits (1,0) by using n(1)PUCCH,1.In this way, actual ACK/NACK message may be connected with combinationof ACK/NACK unit selection and the bit value in the ACK/NACK unit,whereby ACK/NACK transmission for the plurality of data units may beperformed using one ACK/NACK unit. Examples illustrated in Table 1 maybe extended for ACK/NACK transmission for three or more data units.

If the maximum number of data units that can be transmitted through agiven physical resource is great, ACK/NACK bundling or ACK/NACKmultiplexing applied to all the data units may cause considerablecomplexity and/or complicated error status. Accordingly, if the maximumnumber of data units is great, restriction or combination of ACK/NACKtransmission scheme is required. Hereinafter, ACK/NACK transmissionscheme according to the embodiment of the present invention will bedescribed with reference to the accompanying drawings.

In this case, the ACK/NACK state represents ACK or NACK state for eachdata unit. Additionally, the ACK/NACK state (result or response) mayrepresent DTX or NACK/DTX. The ACK/NACK state may include a single bitor a plurality of bits on the basis of Spatial Division Multiple Access(SDMA) transmission, for example.

In the mean time, in this specification, the ACK/NACK signal representsa physical signal transmitted through a physical channel. Unlessmentioned specifically, in this specification, the ACK/NACK state, theACK/NACK result or the ACK/NACK signal may simply be referred to asACK/NACK and may be used together depending on the context.

In this case, a transport channel for ACK/NACK transmission is based oncode-division multiplexing such as PUCCH format 1 series used in thecurrent LTE/LTE-A system, peak-to-average power ratio/cubic metric(PAPR/CM) characteristics may be reduced due to multiple transportchannels.

Moreover, in the LTE-A system, as the user equipment uses multiple CCsfrom a downlink component carrier (DL CC) or uplink component carrier(UL CC), system bandwidth extension has been required. However, theLTE-A user equipment should transmit multiple feedback informationtogether with aggregated carriers as compared with feedback informationtransmitted from the existing LTE user equipment, and the number ofACK/NACK states for acknowledgement based on usage of multiple carriershas been increased.

For example, if N DL CCs used for downlink traffic transmission exist,the user equipment needs to respond to each DL CC by using N ACK/NACKsignals, and an uplink control channel corresponding to a feedbackinformation rate required to transmit the ACK/NACK signals should exist.

However, in the existing legacy control channel structure, since theincreased ACK/NACK signal transmission cannot be satisfied by a feedbackinformation rate based on a single control channel structure, requiredcontrol channel resource regions may be increased and resourceconsumption used for ACK/NACK feedback transmission may be increased,whereby resource waste may be caused.

Accordingly, studies on a method for efficiently transmitting ACK/NACKsignal from a user equipment of an LTE-A system are ongoing. Forexample, a feedback information rate such as ACK/NACK signal may beminimized in a unit of subframe such that too many uplink controlchannels or control information spaces may not be required in a unit ofsubframe.

An example of a method for efficiently transmitting ACK/NACK signal froma receiver of an LTE-A system may include a method for dividing afeedback information rate into group unit information in accordance withone embodiment of the present invention. For example, if the number ofACK/NACK bits to be fed back from the user equipment is N(N>==1), N bitsmay be grouped into M(M>==1) ACK/NACK groups, and the number of ACK/NACKbits allocated to each group may be the same or not the same as oneanother.

Alternatively, an example of a method for efficiently transmittingACK/NACK signal from a receiver of an LTE-A system may include a methodfor reducing a feedback information rate by reducing ACK/NACK states inaccordance with another embodiment of the present invention. At thistime, reduction of the ACK/NACK states may be applied to each groupindependently or may be joined to each group in accordance with atransmission mode.

Hereinafter, in this specification, the aforementioned ‘ACK/NACK state’represents the result of acknowledgement for the data unit (for example,codeword), and includes ACK, NACK or DTX. ACK represents that thereceived codeword has no error, NACK represents that the receivedcodeword has an error, and DTX means that the receiver fails torecognize that the data unit has been transmitted from the transmitter.

1. First Embodiment ACK/NACK State Reduction

The method for efficiently transmitting ACK/NACK signal in accordancewith the embodiments of the present invention may be used for a MIMOtransmission mode where multiple codewords are transmitted at the sametime.

If multiple codewords are used for the MIMO transmission mode,combination of ACK/NACK/DTX indicating acknowledgement of the multiplecodewords may be expressed by one state from feedback information.Moreover, if multiple carriers are used for burst traffic transmission,ACK/NACK/DTX combination may be expressed by a pow function thatincludes three components. In other words, the ACK/NACK state may beexpressed in a type of pow(3, N_(m)*N_(c))1*3, wherein N_(m) means thenumber of codewords in a unit of carrier, N_(c) means the number of usedcarriers, and pow(a, b) represents a^(b).

However, if the existing ACK/NACK state is used for the MIMOtransmission mode, the ACK/NACK state may be represented by three statesof {{ACK}, {NACK}, {DTX}} or two states of {{ACK}, {NACK/DTX}} forsingle codeword transmission. For another example, the ACK/NACK statefor two codewords may be represented by five states of {{ACK, ACK},{ACK, NACK}, {NACK, ACK}, {NACK, NACK}, {DTX}}. Then, if data arereceived through Nc CCs, all the ACK/NACK states that can be used byACK/NACK feedback information may become pow(3, Nc) for single codewordtransmission and pow(5, Nc) for transmission of two codewords.Accordingly, if transmission of Nm codewords can be performed for eachof component carriers, the basic number of ACK/NACK states may begeneralized by pow(2*Nm)+1, Nc).

In the mean time, the PUCCH format 1 provides information space of fivestates in a unit of resource element. Accordingly, if the number ofcodewords in a unit of carrier is (Nm<=2), a single PUCCH resource maybe used for feedback transmission for the codeword received through asingle carrier. One of methods for extending PUCCH resources inaccordance with increase of feedback information is to use Nc PUCCHresources for uplink control feedback. As Nc PUCCH resources arereserved and at the same time Nc PUCCHs are transmitted, combination ofall the ACK/NACK states may be fed back.

However, multiple PUCCH transmission may deteriorate PAPR/CM indicatingsystem throughput as described above, and may reduce uplink cellcoverage.

Accordingly, it is general that one PUCCH is transmitted in a unit oftransmitting antenna or power amplifier. In this case, the number ofinformation spaces available in the limited PUCCH resource isproportional to the number Nc of used carriers. This means that thenumber of feedback information should be reduced to be limited to acertain number of PUCCH resources even though more PUCCH resources areused to satisfy the same number of ACK/NACK bits or only one PUCCH isallocated to an antenna or power amplifier.

Hereinafter, a method for reducing a feedback information rate byreducing ACK/NACK states in accordance with one embodiment of thepresent invention will be described.

As an example of a method for reducing feedback information, feedbackinformation message may be compressed within the range that systemoperation is not limited. If ACK/NACK is fed back and ACK/NACK statesconfigured by combination in accordance with a plurality of codewordssatisfy a given condition, they may be configured by a single state ofone ACK or NACK. For example, if the probability of the occurrence ofNACK is p, the probability of NACK event may be expressed by thefollowing Equation 2.P(k)=NchooseK(Nm*Nc,k)(1−p)^(Nm*Nc−k)*p^k  [Equation 2]

In this case, Nm represents the number of codewords, Nc represents thenumber of aggregated carriers, k represents the number of NACKs ofACKs/NACKs for a plurality of codewords constituting Nc carriers, andNchooseK(a,b)=aCb is obtained. If p is the probability of the occurrenceof NACK, (1−p) represents the probability of the occurrence of ACK.

In the above Equation 2, it is assumed that Nm=2, Nc=4, and p=0.1. Inthis case, P(k) indicating the probability of NACK event may have valuesdistributed as expressed by the following Table 3.

TABLE 3 P(k) = NchooseK(Nm*Nc, k)(1-p){circumflex over( )}(Nm*Nc-k)*p{circumflex over ( )}k, (assume Nm = 2, Nc = 4, p = 0.1)P(k = 0) = 0.43047 P(k = 1) = 0.38264 P(k = 2) = 0.1488 P(k = 3) =0.033067 P(k = 4) = 0.0045927 P(k = 5) = 0.00040824 P(k = 6) =2.268e−005 P(k = 7) = 7.2e−007 P(k = 8) = 1e−008

Referring to Table 3, among the distributed values of P(k) indicatingthe probability of NACK event, it is noted that the probability of oneACK/NACK state including a certain number of NACKs has a very smallvalue that can be disregarded as compared with the probability of otherstate. For example, the ACK/NACK state corresponding to P(k) less than4% may be represented by single NACK regardless of the number ofcodewords corresponding to the corresponding ACK/NACK state, or may notinclude a separate ACK signal. In other words, in Table 3, the state ofP(k>=5) may be disregarded. Accordingly, the ACK/NACK state may becompressed more simply.

FIG. 10 is a flow chart illustrating an example of a procedure oftransmitting feedback information by determining ACK/NACK state inaccordance with one embodiment of the present invention.

Referring to FIG. 10, the user equipment receives one or more carriers,which include one or more codewords, from the base station (S1001).

The user equipment configures entire ACK/NACK states by calculatingACK/NACK for a certain number of codewords by using the number Nc ofused carriers and the number Nm of codewords per received carrier(S1002).

As described above, the ACK/NACK state represents a specific stateconfigured by combination of ACK/NACK/DTX for each of a plurality ofcodewords. The number of entire ACK/NACK states for one or morecodewords may be configured in various manners in accordance with Nm*Nc.In this case, each ACK/NACK state may be configured by combination ofthe received results (ACK/NACK/DTX) for each codeword.

Next, the user equipment determines a predetermined reference value thatcan regard the state of ACK/NACK combination as one NACK or DTX byobtaining the probability P(k) of the occurrence of each ACK/NACK stateof combination of ACK/NACK/DTX for Nm*Nc (S1003).

At this time, the probability of the occurrence of ACK/NACK state may becalculated busing the Equation 1. A predetermined value for regardingthe state represented by combination of {ACK, NACK, DTX} as NACK or DTXmay be set to a certain numbered probability value from the uppermost ina probability distribution of the entire states that may occur, byconsidering bits allocated for feedback transmission from the uplink. Ifthe presence probability of the ACK/NACK state comprised of ACK/NACK/DTXfor each codeword is less than a certain reference, the number of NACKsthat may be included in one ACK/NACK state is determined using apredetermined value, wherein the one ACK/NACK state may regard theACK/NACK state comprised of combination of ACK/NACK/DTX as NACK or DTXof a single state.

A simplified ACK/NACK state is configured using the predetermined valuedetermined at the step S1003 for the ACK/NACK states configured at thestep S1002 (S1004 to S1006). If the number of NACKs included in theACK/NACK/DTX combination state constituting one ACK/NACK is more thanthe reference value, the corresponding ACK/NACK state is configured bysingle NACK/DTX (S1005). On the other hand, if the number of NACKsincluded in the corresponding ACK/NACK state is less than the referencevalue, the corresponding ACK/NACK state is maintained as it is, wherebymultiple ACK/NACK states are transmitted (S1006). An example of themultiple ACK/NACK states or the single ACK/NACK state is illustrated inTable 4.

The ACK/NACK state configured as above is fed back to the base station(S1007). At this time, as the number of ACK/NACK states that may beconfigured per the number of corresponding codewords is reduced, PUCCHresources required to transmit control information such as ACK/NACK maybe reduced.

If the ACK/NACK states are reduced in accordance with FIG. 10, they maybe configured as illustrated in Table 4.

Table 4 illustrates an example of ACK/NACK state configured inaccordance with codewords belonging to a carrier according to oneembodiment of the present invention.

TABLE 4 Reference The value of the number of Available ACK/NACK statesNm*Nc number of N/D N/D states (A = ack, N = NACK, D = DTX, S = Special,/= or) 1 N/A 3 ACK(A), NACK(N), DTX(D) 2 N/A 5 {A, A}, {A, N/D}, {N/D,A}, {N, N}, D 3 2 5 or 9 {A, A, A}, {A, A, N/D}, {A, N/D, A}, {N/D, A,A}, N/D 4 2 6~9 {A, A, A, A}, {A, A, A, N/D}, {A, A, N/D, A}, {A, N/D,A, A}, {N/D, A, A, A}, N/D, S1, S2, S3 5 2 7~9 {A, A, A, A, A}, {A, A,A, A, N/D}, {A, A, A, N/D, A} {A, A, N/D, A, A}, {A, N/D, A, A, A},{N/D, A, A, A, A}, N/D, S1, S2 . . . . . . . . . . . .

Table 4 is an example for description of a method for reducing ACK/NACKstates according to one embodiment of the present invention. In Table 4,the number of states and reference values for NACK or DTX are onlyexemplary, and thus are not limited to examples of Table 4.

In Table 4, incase of Nm*Nc=3, ACK/NACK states for three codewords maybe represented by nine states of{{A,A,A},{A,A,N/D},{A,N/D,A},{N/D,A,A},{A,N/D,N/D},{N/D,A,N/D},{N/D,N/D,A},{N,N,N},N/D}.At this time, if a reference value that may be regarded as one NACK orDTX is determined as 2, the ACK/NACK states, which include two or moreN/D, among a total of nine ACK/NACK states, may be regarded as singlestates of N/D. Accordingly, the ACK/NACK states for three codewords maybe reduced to five of {A,A,N/D},{A,N/D,A},{N/D,A,A},N/D}. In otherwords, the number of ACK/NACK states may be varied depending on thereference value for regarding N/D and the number of codewords.

In Table 4, ‘S’ represents a special state that may be used for specialfeedback information. For example, if user equipment-specific,cell-specific and carrier-specific traffic, which may be definedindependently, are transmitted, corresponding ACK/NACK information maybe defined to be represented by the state ‘S’ regardless of otherACK/NACK information. This situation occurs when primary carrier/anchorcarrier/reference carrier traffic are scheduled. Then, if the userequipment receives the corresponding carrier and successfully decodesthe received carrier (that is, if ACK transmission is definite), it mayreport the state on ACK/NACK information related to a specific carrieror traffic included in the corresponding carrier.

The special state corresponding to special feedback information may berepresented by one or more states (for example, S1, S2, . . . ), and maybe defined as multiple state corresponding to multiple information ormultiple specific carrier/traffic information. If the special state isused, link connection may be maintained even if there is no reliabilityin other carrier traffic.

In order to uniformly maintain a transmission type of ACK/NACKtransmitted through the PUCCH, it is preferable that the special stateis mapped into the PUCCH format used for ACK/NACK transmission. Forexample, if Nr PUCCH resources are used for PUCCH transmission, thespecial state may be mapped into a specific PUCCH (for example, thelowest PUCCH index or legacy PUCCH index based on the lowest CCE of thefirst PUCCH resource or PUCCH index in view of resource allocation).Then, the same resource and state may indicate the same feedbackinformation regardless of the number of allocated resources.

2. Second Embodiment ACK/NACK Bundling Depending on Carrier Type

Generally, when multiple carriers are aggregated, a plurality ofcomponent carriers may have their respective features. For example,among a plurality of component carriers (CCs), some CC may be used forsystem information transmission, and another CC may be used to receive aspecific command from the base station, and the other CC may be used fordata traffic transmission only. Alternatively, there may be CC used totransmit additional information for primary CC for better quality ofservice (QoS). The CCs include stand-alone carriers, backward compatiblecarriers, non-backward compatible carriers and extension carriersdepending on their type.

In more detail, carriers, which may allow a random cell, base station oruser equipment on a relay node to independently perform a procedure forbasic access, cell search and system information transmission throughdefinition of the same physical channel and physical signal as those ofthe LTE Rel-8 carriers, may be defined as the stand-alone carriers. Inthis case, the stand-alone carriers include the backward compatiblecarriers and the non-backward compatible carriers as described above.

The backward compatible carriers are carriers for supporting theexisting legacy system, and may be defined as the carrier that may beaccessed by the LTE user equipment. The backward compatible carriers maybe operated as a part of carrier aggregation or single carrier, andalways exist in pairs (for example, uplink and downlink) in the FDDmode.

The non-backward carriers are those that may not be accessed by the userequipment belonging to the existing legacy system. In other words, thenon-backward carriers may be carriers that may not be used throughcompatibility between the legacy system and the current system. Thenon-backward carriers may be operated as single carriers ifnon-compatibility between the existing system and the current system iscaused by duplex distance. The non-backward carriers may be operated asa part of carrier aggregation if not so.

The extension carriers may not be operated independently, and may bedefined as those used for bandwidth extension only. Unlike thestand-alone carriers, the extension carriers may be regarded as thosehaving non-stand-alone features that do not support the aforementionedprocedures (i.e., at least a part of basic access, cell search andsystem information transmission).

Moreover, the carrier type may be classified into primarycarriers/anchor carriers/reference carriers and secondary carriers.Among the carriers, a special CC related with that the user equipmentthoroughly reports feedback information on the carriers to the basestation may be defined.

In the method for efficiently transmitting feedback information inaccordance with another embodiment of the present invention, thefeedback information is divided into special information and normalfeedback information, and downlink component carriers (DL CCs) used totransmit each information are grouped into a plurality of groups andsubjected to bundling or joint coding as one type of feedbackinformation.

FIG. 11 is a diagram illustrating an example of a plurality of downlinkcarriers aggregated for feedback information transmission according toanother embodiment of the present invention.

Referring to FIG. 11, when four DL CCs are configured in accordance withcarrier aggregation, one (for example, DL CC1) of the four DL CCs may beset to specific CC differentiated from other DL CC used for general datatransmission. Grouped data included in the DL CC1 corresponding to thespecific CC are differentiated from grouped data transmitted through DLCC2 to DL CC4 corresponding to another type DL CC, whereby separatefeedback information may be generated. In other words, feedbackinformation for the special CC may be configured by ACK/NACK state foreach codeword transmitted through the special CC. At this time, thefeedback information for the special CC may be configured as one or morededicated states independently from the other DL CCs.

Data transmitted through the other three DL CCs (for example, DL CC2 toDL CC4) may be grouped through bundling or joint coding as one feedbackinformation during transmission of general feedback information such asACK/NACK feedback information.

FIG. 11 is an example for description of grouping of feedbackinformation according to one embodiment of the present invention. Thespecial CC and the number of the other CCs may be configured differentlyfrom FIG. 11.

FIG. 12 and FIG. 13 are diagrams illustrating other examples of aplurality of downlink carriers aggregated for feedback informationtransmission according to another embodiment of the present invention.

Referring to FIG. 12, the DL CC for transmitting special information isdifferentiated from DL CC for transmitting generally grouped data in thesame manner as FIG. 11, whereby DL CC1 and DL CC2 may be allocated tothe special CC.

Likewise, ACK/NACK signals for codewords transmitted through each DL CCmay be configured, and feedback information may be grouped in such amanner that special information may be differentiated from general data.Feedback information that includes ACK/NACK corresponding to DL CC3 andDL CC4 may be subjected to bundling or joint coding, whereby thefeedback information rate may be reduced. The DL CC1 and the DL CC2corresponding to the special CCs may be configured in such a manner thattheir respective feedback information may be transmitted independently.

Unlike FIG. 12, bundling or joint coding may be applied to the specialinformation, whereby the feedback information rate may be reduced, asshown in FIG. 13. In other words, bundling or joint coding may beperformed for the DL CC1 and the DL CC2 corresponding to the specialCCs.

As described above, the bundled feedback information such as ACK/NACK inaccordance with the aforementioned embodiments described with referenceto FIG. 11 to FIG. 13 may be aggregated as one ACK/NACK state or twoACK/NACK states in accordance with a MIMO transmission mode (forexample, the number of codewords).

In the mean time, bundling may be defined as the reduced feedbackinformation state, and the reduced feedback information may be definedas a part of all the available states in spite of the grouped DL CCs,whereby the number of requested states may be reduced as illustrated inTable 4 or Table 5 below.

3. Third Embodiment The Number of ACK/NACK States

According to still another embodiment of the present invention, a totalnumber of feedback states for respective carriers are configured equallyregardless of the number of aggregated carriers.

If the number of available states in one PUCCH is Ns, the number offeedback information states may be equal to or smaller than Ns. Forexample, if the number of available states in Nc PUCCH resources is Ns′,channel selection may be performed such that the number of feedbackinformation states is less than Ns′.

Accordingly, the number of states based on carrier aggregation may bedefined based on the number of used PUCCHs. For example, if one legacyPUCCH resource is used, three or five states may be represented byACK/NACK feedback that includes DTX. For another example, if two legacyPUCCH resources are used for resource selection, maximum nine statesincluding DTX may be represented. Accordingly, in order to use the samePUCCH resource allocation mode regardless of carrier aggregation level,the method for reducing the feedback information state may be defined insuch a manner that the number of feedback states for carrier aggregationis the same as the number of used PUCCH resources.

Table 5 illustrates another example of ACK/NACK states configured inaccordance with codewords belonging to the carriers according to oneembodiment of the present invention. In Table 5, a state used forfeedback information transmission includes a special state, and thenumber of available states per PUCCH is fixed.

TABLE 5 The number of CCs First PUCCH (fixed to five states) SecondPUCCH (fixed nine states) 1 A, N, D, S1, S2 A, N, DTX, S1, S2, S3, S4,S5, S6 2 {A, A}, {A, N/D}, {N/D, A}, {N, N}, D {A, A}, {A, N}, {N, A},{N, N}, {A, D}, {D, A}, D, S1, S2 3 {A, A, A}, {A, A, N/D}, {A, N/D, A},Embodiment 1) {N/D, A, A}, N/D {A, A, A}, {A, A, N}, {A, N, A}, {N, A,A}, {A, A, D}, {A, D, A}, {D, A, A}, N, D Embodiment 2) {A, A, A}, {A,A, N/D}, {A, N/D, A}, {N/D, A, A,}, N, D, S1, S2, S3 4 {A, A, A, A}, {A,A, A, N/D}, {A, A, N/D, {A, A, A, A}, {A, A, A, N/D}, A/N/D},{A, N/D,A/N/D, A/N/D}, N/D {A, A, N/D, A}, {A, N/D, A, A, A}, {N/D, A, A, A}, N,D, S1, S2 5 {A, A, A, A, A}, {A, A, A, N/D, A/N/D}, {A, A, A, A, A}, {A,A, A, A, N/D}, {A, A, N/D, A/N/D, A/N/D}, {A,N/D, {A, A, A, N/D, A}, {A,A, N/D, A, A}, A/N/D, A/N/D, A/N/D}, N/D {A, N/D, A, A, A}, {N/D, A, A,A, A}, N, D, S

Referring to Table 5, it is noted that one PUCCH may be used and two ormore PUCCHs may be used.

For example, in case of the legacy mode, a feedback informationtransmission mode based on one PUCCH may be used in a single carriermode as the feedback information transmission mode used in the legacysystem. If one PUCCH is used, spaces for uplink data transmission may bedefined as maximum five.

However, if carrier aggregation is performed in the LTE-A system, statesrequired for feedback information transmission are beyond the range ofsingle PUCCH performance. In order to prevent this situation fromoccurring, it is assumed that two PUCCHs are configured in accordancewith still another embodiment of the present invention. In this case,maximum nine ACK/NACK states may be configured regardless of the numberof CCs illustrated in Table 5.

As a result, as the number of states for feedback transmission issimplified as compared with the related art, feedback information thatsatisfies control channel performance may be configured in the LTE/LTE-Asystem.

In Table 5, the special state (S) may be used for a specific usage suchas specific feedback information transmission or may not be used in auseful state. In other words, if the special state is used for specificfunction or specific feedback information transmission, it becomes auseful state and then may be used by the user equipment. If not so, thespecial state may be disregarded and may be processed in a invalidstate.

4. Fourth Embodiment Feedback Information in MIMO Extension

In a system that uses MIMO transmitting antennas, MIMO transmittingantennas may be used to transmit an uplink signal through the PUCCH.

At this time, feedback information according to the embodiments of thepresent invention may be configured differently depending on a symboltransmitted per antenna.

First of all, an example that the MIMO transmitting antennas transmitthe same symbol will be described. For example, if PUCCH modulation forthe MIMO transmitting antennas is configured in the same modulation modeand the same control information is transmitted through eachtransmitting antenna, the MIMO transmitting antennas may be used for aspecial diversity mode. As a result, different PUCCH resources on eachtransmitting antenna may be used as orthogonal transmission resourcesfor identifying channels of a pair of transmitting-receiving antennasfrom each other.

Second, an example that symbols transmitted per MIMO antenna areconfigured differently will be described. If other control informationor joint coded information symbols are transmitted per transmittingantenna, each of the control information may be transmitted throughdifferent PUCCH resources and may be transmitted independently for thetransmitting antennas.

In other words, if the number of codewords is more than one, feedbackinformation of each of the codewords may be mapped into differenttransmitting antennas.

The feedback information may be classified depending on a carrier typeon the basis of the component carriers. In other words, feedbackinformation for each carrier may be mapped into its respectivetransmitting antenna that uses an antenna-specific PUCCH resource.

As described above, the base station and the user equipment throughwhich the embodiments of the present invention can be carried out willbe described with reference to FIG. 14.

FIG. 14 is a block diagram illustrating a base station and a userequipment, through which the embodiments of the present invention can becarried out.

The user equipment may be operated as a transmitter on an uplink and asa receiver on a downlink. Also, the base station ABS may be operated asa receiver on the uplink and as a transmitter on the downlink. In otherwords, each of the user equipment and the base station may include atransmitter and a receiver for transmission of information or data.

The transmitter and the receiver may include a processor, modules,parts, and/or means for implementing the embodiments of the presentinvention. Especially, the transmitter and the receiver may include amodule (means) for encrypting messages, a module for interpretingencrypted messages, an antenna for transmitting and receiving messages,etc.

Referring to FIG. 14, the left part corresponds to a structure of thetransmitter, and the right part corresponds to a structure of thereceiver and represents the user equipment that enters a cell served bythe base station. Each of the transmitter and the receiver may includean antenna 1401 or 1402, a Reception (Rx) module 1410 or 1420, aprocessor 1430 or 1440, a Transmission (Tx) module 1450 or 146, and amemory 1470 or 1480.

The antenna 1401 or 1402 includes a receiving antenna receiving radiofrequency (RF) signals and transferring the RF signals to the Rx module1410 or 1420 and a transmitting antenna transmitting the signalsgenerated from the Tx module 1450 or 1460 to the outside. If a MultipleInput Multiple Output (MIMO) function is supported, two or more antennasmay be provided.

The Rx module 1410 or 1420 may perform predetermined coding anddemodulation for the RF signals externally received through the antennato recover original data and then transfer the recovered data to theprocessor 1430 or 1440. The Rx module and the antenna may beincorporated into a receiving portion for receiving the RF signal unlikeFIG. 12.

The processor 1430 or 1440 generally controls the overall operation ofthe transmitter or the receiver. In particular, the processor 1430 or1440 may perform a controller function for implementing theaforementioned embodiments of the present invention, a variable MediumAccess Control (MAC) frame control function based on servicecharacteristics and a propagation environment, a handover (HO) function,an authentication and encryption function, etc.

The Tx module 1450 or 1460 may perform predetermined coding andmodulation for data, which are scheduled from the processor 1430, 1440and then transmitted to the outside, and then may transfer the coded andmodulated data to the antenna. The Tx module and the antenna may beincorporated into a transmitting portion for transmitting the radiosignal unlike FIG. 11.

The memory 1470 or 1480 may store a program for processing and controlof the processor 1430 or 1440, or may perform a function for temporarilystoring input/output data (uplink (UL) grant allocated from the basestation in case of the user equipment), system information, base stationidentifier (STID), flow identifier (FID), and action time.

Also, the memory 1470 or 1480 may include at least one type of storagemedia such as a flash memory, a hard disk, a multimedia card micro, acard-type memory (e.g. a Secure Digital (SD) or eXtreme Digital (XD)memory), a Random Access Memory (RAM), a Static Random Access Memory(SRAM), a Read-Only Memory (ROM), an Electrically Erasable ProgrammableRead-Only Memory (EEPROM), a Programmable Read-Only Memory (PROM), amagnetic memory, a magnetic disc, an optical disc, etc.

The processor 1430 of the transmitter performs the whole controloperation for the base station. Also, the processor 1430 of thetransmitter may determine whether to retransmit the same signal or nextsignal to the receiver depending on whether a signal received throughthe Rx module 1410 is ACK/NACK/DTX.

If the signal received through the Rx module 1410 is the ACK signal, itindicates that the signal transmitted from the transmitter has beensuccessfully transmitted and decoded. Accordingly, it is not required toretransmit the same signal. On the other hand, if the signal receivedthrough the Rx module 1410 is the NACK signal or DTX signal, itindicates that transmission of the signal transmitted from thetransmitter has been failed. Accordingly, it is required to retransmitthe same signal.

The processor 1440 of the receiver performs the whole control operationfor the user equipment. Also, in order reduce a feedback informationrate when feedback information is generated in accordance with theaforementioned embodiments of the present invention described withreference to FIG. 7 to FIG. 10, the processor 1440 of the receiver mayuse reduced ACK/NACK states in accordance with a predetermined rule ormay perform bundling or joint coding for a plurality of ACK/NACK/DTXinformation using one signal received through the Rx module.

In more detail, the processor 1440 of the receiver determines ACK/NACKstates for each of a plurality of data units received through the Rxmodule 1420. If the plurality of ACK/NACK states include a certainnumber of NACKs, they may be configured in a single NACK state.

Also, the processor 1440 of the receiver may configure the plurality ofACK/NACK states in the multiple ACK/NACK states or the single ACK/NACKstate on the basis of carrier group. At this time, control informationsuch as ACK/NACK states may be configured per carrier, and controlinformation transmitted through different carriers may be multiplexed onthe basis of the carrier group in accordance with a type of each of theplurality of carriers.

The processor 1430 or 1440 may be configured to transmit theaforementioned control information described in the embodiments of thepresent invention through separate signaling not DM-RS. In the meantime, the base station may perform a control function for performing theaforementioned embodiments of the present invention, an orthogonalfrequency division multiple access (OFDMA) packet scheduling, timedivision duplex (TDD) packet scheduling and channel multiplexingfunction, a medium access control (MAC) frame variable control functionbased on service characteristics and radio wave condition, a quicktraffic real-time control function, a handover function, anauthentication and encryption function, a packet modulation anddemodulation function for data transmission, a quick packet channelcoding function and a real-time modem control function through at leastone of the aforementioned modules, or may further include a separatemeans, module, or part for performing the aforementioned functions.

It will be apparent to those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit and essential characteristics of the invention. Thus, theabove embodiments are to be considered in all respects as illustrativeand not restrictive. The scope of the invention should be determined byreasonable interpretation of the appended claims and all change whichcomes within the equivalent scope of the invention are included in thescope of the invention.

The above embodiments are therefore to be construed in all aspects asillustrative and not restrictive. The scope of the invention should bedetermined by the appended claims and their legal equivalents, not bythe above description, and all changes coming within the meaning andequivalency range of the appended claims are intended to be embracedtherein.

INDUSTRIAL APPLICABILITY

The embodiments of the present invention may be applied to variouswireless communication systems. Examples of the various wirelesscommunication systems include 3GPP (3rd Generation Partnership Project),3GPP2 and/or IEEE 802.xx (Institute of Electrical and ElectronicEngineers 802) system. The embodiments of the present invention may beapplied to all the technical fields based on the various wireless accesssystems, as well as the various wireless access systems.

The invention claimed is:
 1. A method for transmitting controlinformation from a user equipment in a wireless communication system,the method comprising: receiving a first physical downlink sharedchannel (PDSCH) on a primary cell and a second PDSCH on a secondary cellconfigured for the user equipment; and transmitting an acknowledgement(ACK)/negative acknowledgement (NACK) feedback for the received firstand second PDSCHs using a selected physical uplink control channel(PUCCH) resource of a plurality of PUCCH resources, wherein the ACK/NACKfeedback indicates a bundle of feedback information for the first PDSCHand feedback information for the second PDSCH, and wherein the bundleindicates respective ACK/NACK states of the first and second PDSCHs. 2.The method according to claim 1, wherein the ACK/NACK feedback isrepresented as 2 bits.
 3. The method according to claim 1, wherein theACK/NACK feedback is transmitted by using PUCCH format 1b.
 4. A userequipment for transmitting control information in a wirelesscommunication system, the user equipment comprising: a transmissionmodule; a reception module configured to receive a first physicaldownlink shared channel (PDSCH) on a primary cell and a second PDSCH ona secondary cell configured for the user equipment; and a processorconfigured to control the transmission module to transmit anacknowledgement (ACK)/negative acknowledgement (NACK) feedback for thereceived first and second PDSCHs using a selected physical uplinkcontrol channel (PUCCH) resource of a plurality of PUCCH resources,wherein the ACK/NACK feedback indicates a bundle of feedback informationfor the first PDSCH and feedback information for the second PDSCH, andwherein the bundle indicates respective ACK/NACK states of the first andsecond PDSCHs.
 5. The user equipment according to claim 4, wherein theACK/NACK feedback is represented as 2 bits.
 6. The user equipmentaccording to claim 4, wherein the ACK/NACK feedback is transmitted byusing PUCCH format 1b.